optical communications optical fiber optical fibers optical literacy optical properties optical signals opticians optimal positioning optimal sewerage system in cities with small elevation optimal weight portfolio optimisation βελτιστοποίηση optimism optimism αισιοδοξία optimization optimization. optoelectronics oracy skills oracy, communication, pronunciation oral communication strategies oral fluency; προφορική γλωσσική ευχέρεια oral health oral hygiene oral narrative speech oral presentations oral production oral proficiency oral skills oral vaccination orality order quantity organ donation organ transplant organ transplant abroad organic and recyclable organic certification organic fraction organic honey certification organic honey price organic matter organic waste organic wastes organisation of school units organisational change organised crime organised play organization organization and innovation management organization and management of Sector Restructuring & Broken Portfolio Management organization and management of schools organizational - transformational learning organizational behavior organizational change organizational change, mental health, personal data, personal data processing organizational climate organizational commitment organizational communication organizational conflicts organizational culture organizational culture, organizational performance, questionaire organizational development organizational education organizational financial performance organizational learning organizational learning culture organizational performance management organizational psychology organizational silence organizational silence-voice, acquiescent silence-voice, defensive silence-voice, prosocial silence-voice, organizational school climate organizational structure organizational structure, leadership, management, organizational culture, job satisfaction organizational voice organizations organization’s performance organized crime origami origin of life original drug orthodox theology orthodoxy orthogonal arrays orthogonal polynomials orthographe ορθογραφία orthographic awareness orthopedic surgery other language students othering otherness out of pocket cost out of trend analysis out-of-school literacies outcome outer space outil pédagogique outils outils numériques outlier detection outliers outpatient neurological clinic outsider outsourcing over 65 years old, dietary habits, economic crisis, elderly diseases over-education overlapping basic service set overqualification overtones overtourism ownership oxidation ozone ozone hole oικονομική κρίση, παιδική υγεία, ποιότητα υγείας, εμβολιασμός oικονομική σταθερότητα oικοσυστημικές υπηρεσίες oπαδική κουλτούρα oπτική άνεση oπτικός γραμματισμός oριζόντια φορολογία. oφθαλμολογία p p-y curves p5.js pH pH και pH pXRF pacifist trend packaging packaging design packaging evaluation packet loss paedagogical impact paediatric ophthalmology pain pain scale painting paired t-tests palliative care pandemic pandemic COVID-19 pandemic Covid 19 pandemic Covid-19 pandemic covid-19 pandemic effects pandemic, COVID-19, crisis, tourism, Greece, economic impact pandemic, economic recession pandemic, labour sector, tele-working pandemic, πανδημία pandemics pandemics covid19 pandémie panel VAR panel analysis panels panhellenic parallel support paramedical paramedical staff parameters that affect renovation project’s management parametric analysis parametric analyzes parametric design parametrisation of normalized axial load vs curvature ductility factor charts parasocial relationships parent meeting parent participation parent training parent training programs parent's attitudes parent-school collaboration parent-school relationship parent-teacher communication parental behaviour types parental education parental emotional expressivity parental empathy parental engagement parental engagement - γονική εμπλοκή parental intervention parental involvement parental involvement in teenagers’ education parental involvement models parental involvement practices parental involvement, refugee/migrant families, ZEP teachers, primary school parental involvement, secondary education, survey, immigrant parents, cultural features, perceptions of teachers parental involvement, teacher attitudes, primary education, Epstein typology parental participation parental perceptions, parent-child relationship, parental acceptance-rejection, special educational needs parental practices parental re-education parental role parental satisfaction parental stress parental style parental support parental typology parental viewpoints parental warmth parenting parenting roles parenting style parents parents - teachers - director - parental involvement - parent associations - effective operation of school parents and teachers' beliefs parents caregivers parents cooperation parents of children with disabilities parents of students parents of typical development children parents perceptions parents' expectatios parents' leadership parents' views parents’ opinions about bilingualism parents’ socio-educational status parent’s role in education parity parking parks parliamentary discourse parody part-time employment partial least squares partial sharing policy participation participation Incentives participation active participation barriers participation in Lifelong Education participation incentive participation motives participation obstacles participation of teachers participation terms participation – building participative leadership participatory design participatory educational techniques participatory educational techniques. participatory learning participatory museum participatory planning. participatory-experiential educational techniques particles particulate mater particulate matter particulate matter (PM2.5 – PM10) particulate matter PM10 & PM2,5 particulate matters particulate pollutants PM10 partitioning graphs partnership in construction partnerships between companies passengers passive leadership passive solar systems passive_systems past victimization pasteurized milk pastoral teaching pastry shop lighting path integrals pathogens of the Greek economy pathological gambling pathophysiology paths patient patient compliance patient flow patient rights, patient complaints, patient protection Services / Health Care Office patient safety patient satisfaction patient satisfaction, satisfaction factors patient-centered medicine patients patients discharge patients satisfaction patients’ safety patients’ satisfaction patriarchal system patriarchy patronage patterns pavement deterioration pavilion pay as you throw pay for performance payment cards payment means payments, electronic payments, payment systems, cards, Capital Controls, Greece payroll system peace tourism peculiarities pedagogical competency programs pedagogical environment pedagogical interaction pedagogical material pedagogical method pedagogical practices pedagogical training pedagogie differenciee, motivations d'apprentissage, role de l'enseignant pedagogy